When operating a wood pulp digester it is important to know the various factors for the control of the wood chip cooking process. Such control is necessary to adjust the digester cooking conditions based on the test results which have been obtained from a previous batch. Thus, in a feedback manner, the tests which have been obtained from a previous batch of wood pulp during a discharge or a "blow" of the wood pulp from a digester are then used to adjust the next batch. Typically, representative samples for laboratory testing are obtained during the discharge cycle of a digester known as a "digester blow". A digester blow lasts about 10 to 15 minutes, typically 12 to 14 minutes and a sample is typically obtained at about 2 minutes from start of a blow at an interval from about 1 minute to about 5 minutes. A typical sample gathering cycle is about 2 minutes throughout the digester blow cycle.
When the samples are conventionally obtained, these show a large variability between the various samples taken at different times from the same digester blow. Replicate testing however on the same sample indicates that the variability of the testing itself is quite small.
It is also known that large industrial digesters digest wood pulp in an inhomogenous manner throughout the chip mass. Infrequent sampling or a single sample obtained during the digester blow cycle represent only a small portion of the batch. Typically, it has been sought to minimize the unrepresentative sampling by taking a composite multiple grab sample over equal increments of time while the batch is being discharged from the digester vessel i.e. during a digester blow. However, unreliable readings are introduced since individuals introduce unacceptable variations in the procedure by their own sampling techniques. Moreover, as the act of sampling itself causes unwanted expelling of gases and hot digester liquor, i.e. digester effluents, the hazards are now ameliorated or minimized in a mill operation employing the novel sampling device.